This invention relates to vehicle seats, and more particularly, to hydraulically controlled seat adjuster and recliner mechanisms for vehicle seats.
In order to accommodate various sizes and shapes of occupants, the front seats of motor vehicles are provided with a fore-and-aft adjustment mechanism to enable occupants to position themselves a desired distance from the vehicle instrument panel, steering wheel and brake pedal. Such seat adjustment mechanisms provide incremental adjustment in the positioning of the vehicle seat. The seat adjustment mechanisms may be manually operable or power operated. In either case, the seat adjustment mechanism includes some means for maintaining the seat in the position to which it has been adjusted.
The manually operable seat adjustment mechanisms presently in use generally include a pair of laterally spaced lower rails which are fixed to the floor of the vehicle and a pair of upper rails slidably mounted on the lower rails. The seat adjustment mechanisms include mechanical devices such as gears, screws, bell cranks and the like to provide relative movement between the upper and lower slide rails in providing fore-and-aft adjustment of the seat. Such mechanisms are awkward to use because the occupant must reach down along the side of the seat and pull up or out on a release lever while shifting the position of the seat. Also, because such mechanisms define a finite number of positions at which the seat can be latched, frequently the seat does not become positively latched in a position to which it has been adjusted. These shortcomings are alleviated to some extent by power seat adjustment mechanisms.
Many power seat adjustment mechanisms utilize a rack and pinion arrangement for moving the seat fore and aft. The seat assembly is attached to a carriage that is slidable along a stationary rack mounted to the vehicle floor pan. The carriage is moved fore and aft by a pinion gear which is driven by a motor and transmission assembly running on a stationary rack. The machining tolerances of the rack and the carriage can result in an uneven meshing of the pinion gear teeth with the rack teeth over the length of travel of the rack. This creates noise and an uneven or jerky motion during the horizontal seat adjustment. For horizontal seat adjustment travel on the order of five inches, the noise and uneven motion is normally within acceptable levels. However, for horizontal seat adjustment travel greater than five inches, the noise level and uneven motion generally exceeds acceptable levels.